Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $93.36   10.730%   $103.3775   $103.38   $103.40   $103.40  
  Purchase #2 $213.92   5.586%   $225.8696   $225.87   $225.85   $225.90  
  Purchase #3 $219.28   4.756%   $229.709   $229.71   $229.70   $229.70  
  Purchase #4 $169.43   8.516%   $183.8587   $183.86   $183.85   $183.90  
  Purchase #5 $232.44   12.577%   $261.674   $261.67   $261.65   $261.70  
  Purchase #6 $188.49   5.852%   $199.5204   $199.52   $199.50   $199.50  
  Purchase #7 $162.68   10.807%   $180.2608   $180.26   $180.25   $180.30  
  7 purchase totals = $1,279.60       $1,384.2700   $1,384.27   $1,384.20   $1,384.40